Fluid measuring system



Sept. 21, 1965 M. L. ARONOW 3,206,978

FLUID MEASURING SYSTEM- Filed July 22, 1963 INVENTOR MaR'rmLHmnuw zwzMATTORNEY United States Patent 3,206,978 FLUID MEASURING SYSTEM Martin L.Aronow, Cherry Hill, N.J., assignor to Schaevitz Engineering, acorporation of New Jersey Substituted for abandoned application Ser. No.781,407,

Dec. 18, 1958. This application July 22, 1963, Ser. No.

1 Claim. (Cl. 73228) This application is a substitute application forapplication, Fluid Measuring System, Serial Number 781,407, filedDecember 18, 195 8, now abandoned.

This invention relates to measuring systems, and more particularly tomass flow meters for fluid measuring systems.

Flow meters are devices or instruments which measure the rates of flowof a liquid or gaseous fluid in a conduit and which produce someindications of the rates of flow. Various difierent types of flow metersare presently in use. Most such flow meters involve a restriction, orprimary device, in the conduit which alters the velocity of the fluidstream and produces a differential pressure. A measuring elementmeasures the differential pressure drop. The pressure drop may betranslated into flow rate readings in numerous ways.

The restrictions that produce the differential pressures may beclassified into general types including orifice, nozzle, venturi andPitot. An orifice is a hole in a thin disk that is inserted betweenflanges in the conduit line. A nozzle is an orifice with a flared orrounded approach section. A venturi, or venturi tube, is a fittingconsisting of a throat preceded by a convergent section and followed bya divergent section. A Pitot, or Pitot tube, is a velocity probe thatreceives the full impact of the fluid stream and converts the entirevelocity head into pressure head.

While such types of flow meters have proved satisfactory in most cases,there have been many instances involving critical measurements in whichthey have not been entirely satisfactory. For example, such types offlow meters produce much pressure drop in the conduit system since theyoften provide a relatively large obstacle to the fluid flow. The Pitottube, while providing the least obstruction to fluid flow in most cases,has the disadvantage of providing an accurate measurement at only onepoint within the conduit and does not integrate over the entire flowarea.

Another disadvantage found in many types of conventional flow meters isthat resulting measurements are affected by changes in static pressure,temperature, viscosity, specific gravity and other variable factors notdirectly related to flow measurements. These changes tend to causeerrors in the measurements relating to mass flow of the fluids involved.

In the case of Pitot tube or other measurement or control devicesinvolving restrictions, changes in viscosity of the fluid may result inclogging of the restrictions thereby introducing errors into a system.

While various correcting means may be employed in mass flow meterdevices to correct for changes in temperature and other variable factorstending to produce erroneous measurement or control signals relating tomass flow, such correcting devices add to the general complexity of thesystem and, in many cases, are not only undesirable but impractical. Forexample, in rocket fuel systems involving the mass flow of liquid oxygento control various functions within a rocket, the measuring and controldevices must be free of errors resulting from changes in static pressureor other variable factors. The mass flow meters involved in rockets,missiles and most aircraft must be relatively simple and minimize theamount of correcting equipment used, since 3,206,978 Patented Sept. 21,1965 such correcting equipment not only takes up space, but adds anotherpossible trouble source to the system.

It is an object of this invention to provide an improved fluid mass flowmeter which is relatively free of errors resulting from changes instatic pressure, specific gravity, temperature or viscosity of the fluidmeasured in a conduit.

It is a further object of this invention to provide an improved fluidmass flow meter which does not involve an obstruction within theconduit.

It is still a further object of this invention to provide an improvedmass flow meter which does not involve probes and in which a resultingmeasurement or control signal is a function of the entire flow within aconduit rather than from a sampling at one or more discrete pointswithin the conduit.

It is still a further object of the invention to provide an improvedmass flow meter which does not involve complex devices for correctionfor changes in static pressure, temperature and other variable functionsnot directly related to mass fluid flow.

It is still a further object of the invention to provide an improvedflow meter device which quicky and accurately responds to changes inmass fluid flow and which is adaptable for use as a control device.

In accordance with the present invention, a mass flow meter is providedwhich is adapted to be used with a conduit having at least two sectionsextending in two different directions. Bellows are disposed in a memberattached at the point adjacent the two divergent sections of the conduitand out of the main path of fluid flow. The bellows responds to changesin mass fluid flow. A differential transformer is associated with thebellows to convert movements of the bellows into appropriate signals formeasurement or control purposes.

Other objects and advantages of the present invention will be apparentand suggest themselves to those skilled in the art to which the presentinvention is related, from a reading of the following specification andclaims, in conjunction with the accompanying drawing, in which:

FIGURE 1 is a side view of a conduit associated with expandable membersshown for the purpose of illustrating the concepts involved in thepresent invention;

FIGURE 2 is a side view illustrating the preferred embodiment of thepresent invention.

Referring particularly to FIGURE 1, a conduit 10 includes sections 12and 14 connected at right angles to each other by an elbow 16. Anexpandible member comprising a bellows 18 is connected between thesection 12 and the elbow 16. A second expandible member or bellows 20 isconnected between the section 14 and the elbow 16.

The bellows 18 and 20 are included in the direct path of the fluid flowwithin the conduit 10 and is, in fact, part of the conduit. When fluidflows through the conduit 10, the elbow 16 may be considered as beingdisposed at point A. When the mass fluid increases in the conduit 10,the resulting pressure change causes the bellows 18' and 20 to expandand the elbow 16 to be moved from point A to point A. The distance movedby the elbow 16 is proportional to pressure change and .a function ofmass flow of the fluid passing through the conduit 10. The motion of theelbow 16 may be measured by suitable transducers.

Since the movement of the elbow 16 is dependent not only upon the massflow of the fluid but also upon various other functions (such as staticpressure) which are subject to change, the device shown is not capableof use as a mass flow meter unless additional correcting means areemployed. If the effects of the elbow movement resulting from staticpressure and other variable conditions are subtracted from the totaleffect of the elbow movement, the movement of the elbow 16 will thenrepresent the mass flow of the fluid within the conduit 10.

illustrated in FIGURE 2.

.measurement or for control purposes. 'of the fitting 28 results fromchanges in mass flow only Referring particularly to FIGURE 2, there isillustrated a mass flow meter that does not respond to variablefunctions, such as static pressure, which are not directly related tomass flow. A conduit 22 includes sections 24'and 26 connected by a Ttype fitting 28. A bellows 30, or other type ,of expandible member, isconnected between the section 24 and the fitting 28. A second bellows 32is connected between the section 26 and the fitting 28.

Extending from the diverging. points of the sections 24 and 26 is athird bellows 34, which is connected between the fitting 28 .and an endmember 36; The end member 36 is held in fixed relationship'to a member38, which is physically fixed to the section 24 of the conduit. A fixedlinkage member 40 connects the two members 36 and 38.

Fixedly mounted on the fitting 28 is a transducer 42 for measuring thedegree of movement of the fitting 28 from point B to point B and totranslate this movement into appropriate signals. The resulting signalsmay be used to indicate a direct measurement of fiuid mass flow or tocontrol the rate of fluid'flow or some other associated function. Thetransducer 42 may be of the differential transformer type which includesa movable core 41 mounted in fixed relationship to the member 38 bymeans of a shaft or pin member 43. ential transformers in which anoutput electrical signal varies linearly with movements of the core arewell known to those skilled in the art.

Consider now the operation of the mass flow meter If we first assumethat the fixed linkage member 40 is not present and the end plate 36were free to move, it may be seen that the fitting 28 will move frompoints B to B' or from B to C in response to changes in both staticpressure and mass flow. This is substantially the type of operationdescribed in connection with FIGURE 1. This,arrangement, as was seen,does not provide a mass flow meter which is independent of variations instatic pressure, temperature of the fluid flowing and other functionsnot directly related to mass fiow.

Consider. now the operation with the fixed linkage member 40 in placeand the end plate 36 maintained in a fixed physical relationship to themember 38. Under these conditions, the fitting 28 will remain at point Band not respond to changes in static pressure, temperature changes inthe fluid, viscosity changes, density changes, and other changes notrelated to mass fluid flow. .The reason is that changes in staticpressure, temperature, viscosity and density result in equal andopposite forces on the fitting 28. Therefore, no movement ,of thebellows results.

In this arrangement, however, the fitting 28 is still capable ofmovement in response to changes in the mass of the fluid flowing. Thusthe fitting 28 may be moved from points B to C, with the movement beinga function of mass flow. The degree of movement may be translated intoappropriatesignals by the transducer 42 for The movement since theforces relating to mass flow are not opposed by forces in oppositedirections.

The operation of the invention may be described in a slightly diiferentmanner. For example, if the T is considered as a free body in space, theforces acting on it are in equilibrium when no fluid is flowing,regardless of the static pressure. No displacement occurs.

However, when flow around the 90 bend occurs at constant volume,additional forces act on the T which Such differare functions of themass of fluid and the acceleration which results from a change indirection of the fluid flow. These forces are resisted by tension inbellows 30 and 32 and by compression in bellows 34. The component offorce and displacement, along the initial direction of flow isproportional to the mass of fluid flowing. The component of force anddisplacement in the transverse direction is of no interest and notmeasured by the transducers.

The flow meter illustrated in FIGURE 2 is essentially free from errorsdue to variations in the specific gravity, temperature or viscosity ofthe fluid flowing. It causes no obstruction in the conduit, such asorifice. or venturi meters, and therefore there is little or noresulting pressure drop from this cause. The flow meter embodying thepresent invention has advantages over Pitot meters or other pressureprobes since it integrates over the entire area rather than takingsamples at one or more discrete points which might not be representativeespecially under turbulent conditions.

- For purposes of clarity, the present invention has been describedprimarily in connection with conduits having sections disposed at rightangles to each other. It is apparent that various different angles ofconduit sections may be employed in practicing the present invention.

It is noted that most fluid systems involve conduits which have a bend.The present invention may, therefore, be incorporated into existingsystems involving such bends without otherwise substantially modifyingthe conduit or piping arrangement involved or introducing obstructionsin the path of fluid flow.

What is claimed is:

In combination with a main fixed fluid conduit having a substantiallyninety degree bend therein to form at least two sections, a movableelement movable with respect to said main fluid conduit included in saidninety degree bend, a bellows forming a portion of each of said sectionsadjacent said bend in said main fluid conduit, means for producing asignal corresponding to the mass flow of a fluid within said conduitcomprising an auxiliary conduit extending from said bend in said mainconduit in substantial alignment with one of said sections of said mainfluid conduit, means for terminating said auxiliary conduit to prevent acontinuous flow of fluid therethrough, means for maintainingtheterminated end of said auxiliary conduit in fixed relationship withsaid main fluid conduit, a bellows included in said auxiliary conduit,said bellows being disposed to be repsonsive to movement of said movableelement due to changes in mass flow of said fluid :and beingnon-responsive to other changing characteristics of said fluid, and adifferential transformer including two elements movable relative to eachother to produce a variable output signal, one of said elements beingconnected in fixed relationship with said main conduit and the other ofsaid elements being connected in fixed relationship with said movableelement for translating movement of said last named bellows intocorresponding electrical siganls.

References Cited by the Examiner UNITED STATES PATENTS 2,538,785 1/51Karig 73228 2,605,638 8/52 Pearson 73--228 2,804,771 9/57 Brown 732282,826,915 3/ 5 8 Libman et a1. 73228 RICHARD C. QUEISSER, PrimaryExaminer.

